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Juvenile foxes were reported earlier in built-up Switzerland—but elevation erased the gap

Research · Ecology

Spring reports containing juvenile Red Foxes (Vulpes vulpes) appeared earlier in Switzerland’s most built-up areas than in its least built-up areas. But the apparent difference largely disappeared when researchers accounted for the country’s elevational structure.

The study analysed 4,295 public reports of red foxes from 2018 to 2024, spread across 496 grid cells measuring 5 × 5 kilometres. Rather than estimating when cubs were born or first left their dens, the researchers compared when the estimated probability that a spring report from each area contained juveniles reached 30%. In the most built-up cells, this threshold was reached about 4.7 days earlier than in the least built-up cells.

The more built-up cells were also at substantially lower elevations. Temperature made little difference to the apparent contrast, but accounting for both elevation and temperature changed the estimate: the most built-up areas were then estimated to reach the threshold 0.7 days later. The uncertainty was wide enough that the data did not establish a clear difference between more and less built-up areas. Because Switzerland’s most built-up cells were also lower, the initial comparison mixed urbanization with geography; the study found no clear independent urban advance in the timing of records containing juveniles. This is version 1 of a preprint and has not yet been peer reviewed.

Sources and image credit

  1. The Apparent Urban Advance in Juvenile Vulpes vulpes Observations Diminishes after Accounting for Switzerland's Elevational StructurePrimærkilde, versjon 1. Repository-oppføringen og sammendraget støtter studiens omfang, hovedresultatene og tolkningen. Arbeidet er ikke fagfellevurdert; fullteksten ble ikke uavhengig kontrollert.

Image: A red fox (Vulpes vulpes) stands in the snow in Rautas fjällurskog, Sweden. Photo: ClaudiaTen / Wikimedia Commons, CC BY-SA 4.0. Representative photograph. · CC BY-SA 4.0 · Source

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